1. Field of the Invention
The present invention relates to a serial-parallel conversion circuit and a display device including the serial-parallel conversion circuit. Further, the present invention relates to a method for driving the serial-parallel conversion circuit.
2. Description of the Related Art
In order to display an image on a display device, a large number of image signals need to be supplied to the display device. Further, a large number of wirings are needed to connect a device for supplying image signals (e.g., a main body of an electronic device) to the display device. For example, about 640 wirings are needed for VGA. Accordingly, the wirings occupy volume in part of the display device, which might limit the flexibility in design such as the size of the electronic device and the position of the display device.
In view of such a background, it is desired that the number of external connection terminals in a display device be reduced. For example, Patent Document 1 discloses a method in which a serial-parallel conversion circuit is provided in a display device and an image signal is supplied as a serial signal from a main body of an electronic device through a serial cable.
Further, a serial-parallel conversion circuit for converting a high-speed serial signal to a parallel signal is desired.
An example of a serial-parallel conversion circuit is shown in FIGS. 7A and 7B. FIG. 7A illustrates the entire structure of a serial-parallel conversion circuit, and FIG. 7B illustrates the structure of a sampling switch of one unit included in the serial-parallel conversion circuit. As shown in FIG. 7A, a serial-parallel conversion circuit 20 includes n (n is a natural number greater than 1) units in each of which a sampling switch and an amplifier are connected in series. For example, in a first unit 10(1), a first sampling switch 11(1) and a first amplifier 12(1) are connected in series. In addition, a first input portion 20a to which a serial signal is input, a second input portion 20b including n connection terminals to which a selection signal for sequentially selecting one unit from the n units is input, and an output portion 20c including n terminals from which a parallel signal is output are included. First input terminals of n sampling switches are each connected to the first input portion 20a. Second input terminals of the n sampling switches are each connected to any one of the n connection terminals included in the second input portion 20b. Output terminals of n amplifiers (specifically an output terminal 20c(1) of the first amplifier 12(1) to an nth output terminal 20c((n)) of the nth amplifier 12((n))) are each connected to any one of the n terminals of the output portion 20c independently. Further, the sampling switch outputs part of the serial signal to the amplifier connected to the sampling switch while being selected by the selection signal. The amplifier amplifies part of the serial signal and outputs the amplified signal from the output terminal. Such a serial-parallel conversion circuit 20 is known.